1. Field of the Invention
The present invention relates to a driving device that supplies a driving signal used for discharging liquid droplets from a nozzle of a liquid discharging head that is represented by an ink jet head and a liquid discharging apparatus and an ink jet recording apparatus that use the driving device.
2. Description of the Related Art
In ink jet recording apparatuses, in order to form images having a high quality, the shape of each dot that configures an image is required to be a perfect circle. Accordingly, a satellite liquid droplet must be prevented from landing at a position away from a landing position of a main liquid droplet. In order to prevent the generation of the satellite liquid droplet, a method in which a resonant period (Helmholtz natural oscillation period) is used in a driving waveform or a method that is based on a combination of consecutive pulses is proposed.
In JP3241352B, an ink jet recording apparatus is disclosed in which one ink dot is formed on a recording sheet by discharging a plurality of ink droplets from one nozzle during one discharge period and integrating the plurality of ink droplets before the ink droplets arrive at the recording sheet.
In the ink jet recording apparatus disclosed in JP3241352B, pulses configuring a reference driving signal are formed as a signal such that a time interval between pulse signals configuring the reference driving signal is configured to be gradually closer to the natural period of an actuator and be gradually lengthened, so that the discharge speed of an ink droplet discharged later is higher than that of an ink droplet discharged previously.
In addition, the ink jet recording apparatus disclosed in JP3241352B is configured such that pulse signals corresponding to the number of ink discharges are selected from the final pulse signal (P5) side among a plurality of pulse signals (P1 to P5) configuring the reference driving signal.
In JP2006-142588A, an image forming apparatus is disclosed which is configured so as to reduce the deterioration of the image quality due to a satellite liquid droplet by discharging a main liquid droplet in accordance with waveform elements S1 to S3, increasing the liquid droplet speed of the satellite liquid droplet accompanied with the main liquid droplet without discharging the main liquid droplet in accordance with waveform elements S4 and S5, and integrating the main liquid droplet and the satellite liquid droplet at a landing position or integrating the satellite liquid droplet with the main liquid droplet during the flight of the main liquid droplet, by using a driving waveform including a waveform element S1 that gradually decreases from a reference electric potential Vref to a voltage Va, a waveform element S2 that maintains the voltage Va after the waveform element S1, a waveform element S3 that rises from the voltage Va to a voltage Vb that is higher than the reference electric potential Vref after the waveform element S2, a waveform element S4 that maintains the voltage Vb between a maintaining time Tw in a range from Tc×(1/2) to Tc×(3/2) for a natural frequency Tc of a liquid chamber after the waveform element S3, and a waveform element S5 that gradually decreases from the voltage Vb to the reference electric potential Vref after the waveform element S4.
In JP2006-188043A, it is disclosed that, by including an expansion pulse used for expanding a pressure generating chamber, a first contraction pulse used for contracting the pressure generating chamber after the expansion pulse, and a second contraction pulse used for contracting the pressure generating chamber after the first contraction pulse and setting the pulse width of the expansion pulse to 0.7 AL to 1.3 AL (here, AL is a half of the acoustic resonant period of the pressure generating chamber) and setting the pulse width of the first contraction pulse to 0.3 AL to 1.5 AL, positive pressure waves according to the contraction can be added together so as to increase the discharge pressure (discharge speed) of the liquid droplet when a negative pressure wave due to the expansion of the pressure generating chamber at the time of starting to apply the expansion pulse is inverted to be a positive pressure wave in 1 AL, and accordingly a discharge force having the highest efficiency is acquired.
In addition, in JP2006-188043A, it is disclosed that one dot (super droplet) is formed by discharging a plurality of ink droplets (sub drops) by continuously applying a series of driving pulses within the same pixel period (within the same driving period) a plurality of times and integrating the ink droplets during flight or after landing.
Furthermore, in JP2009-286108A, an apparatus is disclosed which can suppress the generation of a satellite liquid droplet by compressing a pressure chamber in two steps by raising the voltage, which has been lowered in a first voltage change process, in two steps of a second voltage change process and a third voltage change process.
In addition, in JP2009-274433A, an apparatus is disclosed which can suppress the generation of a satellite liquid droplet by adjusting the speed of a liquid droplet.